| //! Module for inferring the variance of type and lifetime parameters. See the [rustc dev guide] |
| //! chapter for more info. |
| //! |
| //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html |
| |
| use hir::Node; |
| use rustc_arena::DroplessArena; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE}; |
| use rustc_middle::ty::query::Providers; |
| use rustc_middle::ty::{self, CrateVariancesMap, TyCtxt}; |
| |
| /// Defines the `TermsContext` basically houses an arena where we can |
| /// allocate terms. |
| mod terms; |
| |
| /// Code to gather up constraints. |
| mod constraints; |
| |
| /// Code to solve constraints and write out the results. |
| mod solve; |
| |
| /// Code to write unit tests of variance. |
| pub mod test; |
| |
| /// Code for transforming variances. |
| mod xform; |
| |
| pub fn provide(providers: &mut Providers) { |
| *providers = Providers { variances_of, crate_variances, ..*providers }; |
| } |
| |
| fn crate_variances(tcx: TyCtxt<'_>, crate_num: CrateNum) -> CrateVariancesMap<'_> { |
| assert_eq!(crate_num, LOCAL_CRATE); |
| let arena = DroplessArena::default(); |
| let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &arena); |
| let constraints_cx = constraints::add_constraints_from_crate(terms_cx); |
| solve::solve_constraints(constraints_cx) |
| } |
| |
| fn variances_of(tcx: TyCtxt<'_>, item_def_id: DefId) -> &[ty::Variance] { |
| let id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local()); |
| let unsupported = || { |
| // Variance not relevant. |
| span_bug!(tcx.hir().span(id), "asked to compute variance for wrong kind of item") |
| }; |
| match tcx.hir().get(id) { |
| Node::Item(item) => match item.kind { |
| hir::ItemKind::Enum(..) |
| | hir::ItemKind::Struct(..) |
| | hir::ItemKind::Union(..) |
| | hir::ItemKind::Fn(..) => {} |
| |
| _ => unsupported(), |
| }, |
| |
| Node::TraitItem(item) => match item.kind { |
| hir::TraitItemKind::Fn(..) => {} |
| |
| _ => unsupported(), |
| }, |
| |
| Node::ImplItem(item) => match item.kind { |
| hir::ImplItemKind::Fn(..) => {} |
| |
| _ => unsupported(), |
| }, |
| |
| Node::ForeignItem(item) => match item.kind { |
| hir::ForeignItemKind::Fn(..) => {} |
| |
| _ => unsupported(), |
| }, |
| |
| Node::Variant(_) | Node::Ctor(..) => {} |
| |
| _ => unsupported(), |
| } |
| |
| // Everything else must be inferred. |
| |
| let crate_map = tcx.crate_variances(LOCAL_CRATE); |
| crate_map.variances.get(&item_def_id).copied().unwrap_or(&[]) |
| } |